Method for the halogenation of benzene



United States Patent 3,128,240 METHQD FOR THE HALOGENATION 0F BENZENE Paul F. Kusy, Moiine, 131., assignor to The Bendix Corporation, a corporation of Delaware No Drawing. Filed May 15, 1959, Ser. No. 813,356 2 Claims. (Cl. 204-154) This invention relates to an improvement in the method of the halogentation of benzene and more particularly relates to an improvement in the method of producing a monohalogen benzene compound.

Present methods for the halogenation of benzene yield principal monohalogen benzene compounds together with the isothermic ortho and para-dihalogenbenzene and other polyhalogenbenzene compounds. The principal compound, monohalogenbenzene, is used in substantial quantities commercially whereas the dihalogenbenzene compounds are of little demand and have limited uses. A monohalogenbenzene such as chlorobenzene, has substantial uses as an intermediate in the manufacture of phenol, aniline, DDT, and dyes whereas the paradichloro benzene may be utilized as an insecticide, moth repell-ant and a deodorant and the orthodichlorobenzene may be utilized to combat termites and as a solvent. Although present methods in the halogenation of benzene may be found where the yield of the monohalogen benzene is approximately seventy percent and the remainder polyhalogenbenzenes and by-products, the resultant quantity of the polyhalogenbenzenes available for sale far outreaches its demand.

An object of the invention is to provide an improved method for the halogenation of benzene.

Another object of the invention is to provide a method for the halogenation of benzene in which the conventional yield is modified by applying sonic energy to the reaction.

A further object of the invention is to provide a method for the halogenation of benzene in which the by-products, the polyhalogenbenzenes, are substantially eliminated by the application of sonic energy to the reaction.

A still further object of the invention is to provide a method for shortening the time required to halogenate benzene by the application of sonic energy to the reaction.

A further object of the invention is to provide a method for the chlorination of benzene in which sonic energy is applied to the reaction and substantially only monochlorobenzene is produced.

These and other objects and advantages of the invention, which will hereinafter be apparent, are realized by applying sonic energy to the reaction in which the normal by-products of polyhalogenbenzenes are substantially eliminated.

As it is used herein, the word sonic refers to a mechanical wave action and may be at frequencies which are either audible or inaudible.

I have discovered that the application of sonic energy to the reaction of a halogen with benzene will alter the expected yield of monohalogenbenzene and the polyhalogenbenzenes. Unexpectedly the end product will comprise substantially no polyhalogenbenzenes which compounds are the undesirable by-products in the commercial production of monohalogenbenzenes. The application of sonic energy to the reaction of 'a halogen and benzene will in addition speed up the reaction, allow the temperature of the reaction to be controlled over a wider range and reduce the amount of catalyst required.

The most reactive of the halogens is chlorine, in the commercial chlorination of benzene an end product of 70% monochlorobenzene, 15% para-dichlorobenzene, 9% benzene and 6% orthodichlorobenzene including other polychlorobenzenes may be obtainable. A reaction 3,128,240 Patented Apr. 7, 1964 ice-r to achieve such an end product would require the selection of the proper catalyst, and a careful control of the temperature and rate of reaction. An example of a commercial process in the chlorination of benzene to produce the above results is as follows. Dried benzene and a catalyst, anhydrous ferric chloride, are combined in a container, chlorine is added to the benzene at a controlled rate while maintaining the temperature of the mixture at 55-60 C. When the mixture attains the required density, approximately 6 hours, the reaction is stopped. During the reaction hydrogen chloride gas is given off. After separation of the products the above percentages of the product will be found which include some unreacted benzene. The commercial method for brornination of benzene is carried out in a similar manner and will result in a slightly lower yield of bromobenzene because of the lower reactivity of bromine to chlorine.

In practicing the invention the quantity of the constituents of the reaction are used substantially in accordance with the proportions of the reaction equation. Benzene and a metallic trihalide are combined in solution. The

catalyst, the metallic trihalide, may very advantageously be selected from the group comprising anhydrous ferric chloride and anhydrous aluminum chloride. Any halogen, advantageously chlorine or bromine, is added slowly to the solution in such proportions that the addition is completed in approximately one hour. The temperature of the reaction is controlled between 40 and 60 C. without regard to the halogen being used. Other periods of time for the addition of the halogen may be used and other ranges of control temperature for the reaction may be used but the time and temperature illustrated will produce superior results. Energy, normally sonic energy, is applied to the reaction suflicient to produce cavitation during the addition of the halogen and after the addition of the halogen until substantially all of the halogen has reacted. Generally cavitation will complete the reaction within one hour following the complete addition of the halogen.

For the purpose of illustration and not of limitation, the following examples are given to illustrate improved methods for the halogenation of benzene in accordance with the invention.

Example I Chlorine is continuously added to a mixture of dried benzene and anhydrous ferric chloride for approximately one hour. The solution is maintained between 40 and 60 C. and sonic energy is applied to the solution sufficient to cavitate said solution during and after the addition of said chlorine. The end product will comprise essentially monochlorobenzene and some unreacted benzene, the end product is a good commercial grade of chlorobenzene. Separation of the end product will give approximately monochlorobenzene and the remainder benzene and polychlorobenzenes.

Example II Bromine is added to a mixture of dried benzene and anhydrous aluminum chloride for approximately one hour. The solution is maintained between 40 and 60 C. and sonic energy is applied to the solution suflicient to cavitate said solution during and after the addition of said bromine. The end product will comprise essentially monobromobenzene and some unreacted benzene, the end represents a good commercial grade of bromobenzene. Separation of the end product Will give approximately 95% monobromobenzene and the remainder benzene and polybromobenzene.

Although only a limited number of examples of the invention have been described, it is to be understood that the invention is not limited thereto. Various changes can 3. be made therein without departing from the spirit and scope of the invention, as the same will be understood by those skilled in the art.

I claim:

1. The method for decreasing the yield of polydichlorobenzene in the chlorination of benzene which comprises the steps of combining benzene and anhydrous ferric chloride in solution, maintaining the temperature of said solution between 40 and 60 0, adding chlorine to said temperature controlled solution while sonically cavitating said solution, washing and drying the product and distilling off the chlorobenzene.

2. The invention defined in claim 1 in which said solution is cavitated for a period not to exceed one hour after the addition of said chlorine to react substantially all of the chlorine.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES American Institute for Chemical Engineers, Ultrasonics Symposium, Series No. 1, volume 47 (1951), pages 22-27. 

1. THE METHOD FOR DECREASING THE YIELD OF POLYDICHLOROBENZENE IN THE CHLORINATION OF BENZEND WHICH COMPRISES THE STEPS OF COMBINING BENZENE AND ANHYDROUS FERRIC CHLORIDE IN SOLUTION, MAINTAINING THE TEMPERATURE OF SAID SOLUTION BETWEEN 40 AND 60*C., ADDING CHLORINE TO SAID TEMPERATURE CONTROLLED SOLUTION WHILE SONICALLY CAVITATING SAID SOLUTION, WASHING AND DRYING THE PRODUCT AND DISTILLING OFF THE CHLOROGENZENE. 